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Horticultural sand and grit

Also known as Sharp sand, Grit sand, Coarse sand, Silica sand

Growing mediumDepends
Sharp sand Photo: MediaMOF · CC BY-SA 4.0

In short

Horticultural sand is washed, coarse, lime-free sand or fine grit used to open up potting mixes and add weight. Only coarse sand helps drainage; fine sand such as play sand can make mixes denser and wetter.

How it looks

Angular grains of quartz or granite, typically pale grey, buff or white, feeling gritty between the fingers. Sand particles range from about 0.05 to 2 mm; medium and coarse grades are the useful ones in pots. The ICPS recommends sharp silica or quartz sand of about 1.5–2 mm for carnivorous-plant mixes.

Signs

A mix with too much fine sand sets hard, drains slowly and can crust on top. Sand with added minerals or lime is unsuitable for carnivorous plants.

What favours it

Coarse sand increases porosity because of its large particles; it is cheap and heavy. Fine sand reduces drainage.

Prevention

  • Use washed, lime-free coarse or sharp sand, not play sand, beach sand or fine plaster sand.
  • For carnivorous plants, use pure washed silica or quartz sand with no added minerals.
  • Combine sand with an organic component rather than using it alone.

Treatment

Start with the first step and move down only if the problem persists.

  1. If a sandy mix has set hard, repot into a mix with more coarse material such as pumice, bark or perlite.

Pros and cons

Pros

  • Adds weight and stability to pots.
  • Coarse grades improve drainage and porosity.
  • Inexpensive and does not decompose.
  • Traditional part of many classic mixes, including John Innes composts.

Cons

  • Heavy.
  • Fine sand reduces drainage and can make mixes denser.
  • Advice differs by use: University of Maryland Extension suggests coarse builder sand for general containers, while the ICPS finds builders, play and plaster sand too fine for carnivorous plants.
  • Holds little water or nutrients.

Look-alikes

Perlite
Perlite is white and much lighter, and floats.
Pumice
Pumice grains are porous and lighter than solid sand grains.

Typical uses

Cacti, succulents, alpines and carnivorous plants; also general mixes such as John Innes and several Clemson foliage-plant recipes.

Sources

  1. Growing Media (Potting Soil) for Containers — University of Maryland Extension
  2. Growing Media — Texas A&M AgriLife Extension, Ornamental Production
  3. Peat, Sand, Perlite — International Carnivorous Plant Society
  4. Indoor Plants – Soil Mixes — Clemson Home & Garden Information Center
  5. John Innes compost — Wikipedia

Written in our own words from these sources. Check a product label before using any treatment.